When you shit your pants and/or don't wipe well. This leads to your ass being caked in shit due to the lack of wiping.
Jason: What is that horrible smell
Brody: Ummmm..I think I had an accident
Jaosn: What the hell happened
Brody: Well, I don't like the toilet paper here so I have not been wiping properly.Here...take a look.
Jason: OMG...You have an ass caked in shit!!!!
1)Having chaffed asshole. When you have wiped your ass a lot, mostly during diarrhea, and you ass has become extremely dry or chaffed.
2)The feeling of having wiped with pine straw.
Cave man 1: Why is Bob walking funny?
Cave man 2: Oh, he has diarrhea and he ran out of leaves so he had to use pine straw to wipe, so he has Cave Ass.
Cave man 1: HAHAHA!